Most conventional carpets comprise a primary backing with yarn tufts in the form of cut or uncut loops extending upwardly from this backing to form a pile surface. For tufted carpets, the yarn is inserted into a primary backing (frequently a woven or nonwoven substrate) by tufting needles and a pre-coat (i.e., a binder) is applied thereto.
Many residential and commercial carpets are also manufactured with a woven scrim (typically made from polypropylene) attached to the back of the carpet to provide dimensional stability to the carpet. These are dual layer products, where two coating layers (precoat for tuft anchorage and adhesive for scrim fixation) are added wet, and the scrim is added afterwards. After fixation of the scrim, the carpet is cured at 130-200° C. for a certain time.
For both the pre-coat and the adhesive layer, the physical properties of the binder are important to their successful utilization as carpet coatings. In this regard, there are a number of important requirements which must be met by such coatings. The coating must be capable of being applied to the carpet and dried using the processes and equipment conventionally employed in the carpet industry for latex, e.g. emulsion, coating. The binder composition must provide excellent adhesion to the pile fibers to secure them firmly in the backing. The coating will also typically have a high loading of fillers such as calcium carbonate, clay, barite, feldspar, cullet, fly ash and/or recycled carpet backing. Further, coatings used as adhesives must also be able to secure substrates to the carpet secondary backing, thereby enabling the preparation of material for use in wall-to-wall carpeting.
The binders in coating and adhesive compositions for carpet materials are frequently emulsion polymers, i.e., latex dispersions, such as styrene-based emulsion copolymers like styrene-butadiene latex (SBL) materials or such as acrylic polymer latex dispersions. U.S. Pat. No. 4,689,256, for example, discloses flame retardant carpet products comprising an acrylic polymer latex used with a polyvinyl chloride (PVC) backing layer.
Copolymers of vinyl esters (such as vinyl acetate and vinyl verstate) and vinyl ester/ethylene can also be used and can frequently have cost and performance advantages such as flame retardancy over styrene-based coatings and adhesives such as SBL. For example, vinyl ester copolymers can be used to provide carpet products which are desirably low in VOC (volatile organic compound) content and which do not contain potentially toxic materials such as 4-phenyl cyclohexene (4-PCH) and related compounds which can be found in styrene-butadiene-based polymer dispersions. Vinyl ester copolymers form carpet coating and adhesive layers which are also advantageously resistant to degradation by visible light and/or ultraviolet (UV) radiation.
Emulsion binders and carpet coating compositions based on vinyl ester/ethylene, e.g., vinyl acetate/ethylene (VAE), copolymers are disclosed, for example, in WO 2010/089142 and in U.S. Pat. Nos. 4,735,986; 5,026,765; 5,849,389; 6,359,076; 7,056,847; 7,582,699; 7,649,067; and in U.S. Patent Application Publication No. 2005/0287336. Some of these patent documents note that such VAE binders and coating compositions are compatible with polyvinyl chloride (PVC) plastisols which are frequently used as backing layers in such carpet products.
The vinyl ester/ethylene copolymers used in the binders and coating compositions described in the foregoing patent documents are prepared by polymerizing appropriate co-monomers in an aqueous emulsion. Such emulsions or dispersions can be stabilized by adding conventional surfactants (anionic, nonionic, cationic) as emulsifiers. Such emulsions or dispersions may also be stabilized by including protective colloids.
Notwithstanding the availability of a variety of carpet coating and adhesive compositions based on stabilized vinyl ester and vinyl ester/ethylene (e.g., VAE) latex emulsion/dispersion binders, it would be advantageous to configure specific types of medium hard (as quantified by copolymer glass transition temperature, Tg), vinyl ester- and VAE-based, filler-containing, environmentally friendly binder emulsions/dispersions which exhibit a desirable balance of properties that make them especially useful in preparing textile structures such as carpets and carpet material. The present development provides carpet products of especially desirable low flammability and low smoke generation properties without adding any external flame retardant additives. This offers the carpet producer the advantage of reduced formulation complexity combined with cost and use benefits. Such carpet products can also be desirably low in volatile organic compound (VOC) content and are advantageously resistant to degradation by light and UV radiation. The carpet products described herein with their VAE-based coatings, binders and adhesives having a selected combination of features (e.g., specific co-monomers, cross-linkers, stabilizers, polymer particle sizes, Tg's, and fillers) can provide such a desirable balance of properties, especially when compared to carpet products using state-of-the-art SBL-based carpet binder and adhesive coatings.